The background of the invention is set forth in two parts: the field of the invention and the description of related art.
1. Field of the Invention
This invention relates to an apparatus and method for bioremediation of groundwater or treatment of wastewater contaminated with dissolved hydrocarbons (such as dissolved alkanes and alkenes), aromatic hydrocarbons (particularly benzene, toluene, ethylbenzene and xylenes) and/or halogenated hydrocarbons (particularly tetrachloroethylene, trichloroethylene, and 1,1,1-trichloroethane). In particular, it relates to biodegradation of such compounds by denitrifying microorganisms.
2. Description of Related Art
The activities of the U.S. Department of Defense (DoD), the U.S. Department of Energy (DOE) and their contractors result in the generation of large amounts of hazardous wastes. Many of the constituents of concern are waterborne or have become waterborne as a result of leaks or spills. Among the most troublesome of these wastes are organic solvents. Even at low concentrations these constituents are often toxic, tend to be resistant to conventional treatment methods and are persistent in the environment.
Most productive research on new biotechnologies for hazardous waste remediation is conducted from a reactor engineering perspective. Grady explained this phenomenon as follows (Grady, C. P. L., Jr. Biological detoxification of hazardous wastes: What do we know? What should we know? In Y. C. Wu (Ed.), Proceedings of the International Conference on Physiochemical and Biological Detoxification of Hazardous Wastes. Lancaster, Pa.: Technomic, 1989, pp. 3-16.):
"Many of the major advances in pollution control technology have come from the application of reactor engineering to wastewater treatment systems. Reactor engineering is based on the premise that, if the kinetics of a reaction can be expressed mathematically, then it is possible to investigate the impact of reactor type and configuration on the extent of reaction through application of mathematical models that incorporate both transport and reaction terms."
The reactor engineering approach involves gathering the information required to mathematically model various process options. Reliance on process modeling offers a number of advantages. First, development of the model in the early stages of the project can facilitate design of the experimental apparatus and procedures. Second, a model provides a framework for understanding the microbiology of the system under study. Finally, a calibrated model is a valuable tool for investigating applications of the knowledge gained during the research for the resulting scale-up of this knowledge.
Recent research has revealed the promise of novel bioremediation schemes that rely in part or totally on anaerobic processes. These include metabolic processes (such as aerobic respiration, denitrification, sulfate reduction and/or methanogenesis) and/or cometabolic processes (such as reductive dechlorination), (Hunter et al. Biomimetic Process for Hazardous Waste Remediation. Phase I Final Technical Report prepared for Defense Advanced Research Projects Agency, YES Inc, 1992).
Biotransformation of some of the compounds of interest applicable to bioremediation process design have been found to occur under denitrifying conditions. Bakker disclosed that a mixed culture can degrade phenol, o-cresol, m-cresol and p-cresol under anaerobic conditions in the presence of nitrate as the terminal electron acceptor (Bakker, G. Anaerobic degradation of aromatic compounds in the presence of nitrate, FEMS Microbiology Letters, 1. 103-108, 1977). Pure cultures of three Gram-negative, slightly curved, monotrichously flagellated rods, including strain DSM 981, were capable of phenol decomposition under anaerobic conditions in the presence of nitrate. Pillis and Davis (in U.S. Pat. No. 4,352,886, Oct. 5, 1982) disclosed a mutant microorganism, Pseudomonas putida CB-173, that is capable of degrading phenolics at a temperature as low as 1.degree. C. to 4.degree. C. at a faster rate than known Pseudomonas putida type strains, and they disclosed a process for treating wastewater containing phenolics using the mutant microorganism strain. Molin and Nilssan disclosed a pseudomonad that is capable of growing in continuous culture with phenol as the only carbon and energy source under aerobic conditions (Molin, G. & Nilssan, I. Degradation of phenol by Pseudomonas putida ATCC 11172 in continuous culture at different ratios of biofilm surface to culture volume, Applied and Environmental Microbiology, 50, 946-950, 1985). Bossert et al. disclosed two bacterial species which utilize p-cresol as the sole source of carbon when grown in a co-culture of both nicroorganisms under nitrate-reducing conditions (Bossert, I. D., Rivera, M. D., & Young, L. Y. p-Cresol biodegradation under denitrifying conditions: Isolation of a bacterial coculture, FEMS Microbiology Ecology. 38, 313-319, 1986). A syntropic relationship was documented. Bossert and Young disclosed metabolism of p-cresol as a sole carbon source under nitrate-reducing conditions by the denitrifying bacterial isolate PC-07 (Bossert, I. D. & Young, L. Y. Anaerobic oxidation of p-cresol by a denitrifying bacterium, Applied and Environmental Microbiology, 52, 1117-1122, 1986). Nitrate was required as the external electron acceptor and was reduced to molecular nitrogen. Phenol, toluene, o-cresol and m-cresol were not metabolized by the isolate.
Tschech and Fuchs disclosed several strains of bacteria which, in the absence of molecular oxygen, oxidized phenol to carbon dioxide with nitrate as the terminal electron acceptor (Tschech, A. & Fuchs, G. Anaerobic degradation of phenol by pure cultures of newly isolated denitrifying pseudomonads, Archives of Microbiology. 148, 213-217, 1987). The bacteria were facultatively-anaerobic Gram-negative rods. Hu and Shieh disclosed removal of phenol and o-cresol under anoxic conditions in an upflow biofilter with nitrate as the electron acceptor (Hu, L. Z. & Shieh, W. K. Anoxic biofilm degradation of monocyclic aromatic compounds, Biotechnology and Bioengineering, 30, 1077-1083, 1987). O-cresol was removed at a slower rate. Major et al. disclosed the biodegradation of benzene, toluene and the isomers of xylene (formerly called BTX) in anaerobic batch microcosms containing shallow aquifer material. Denitrification was confirmed by nitrous oxide accumulation after acetylene blockage of nitrate reductase (Major, D. W., Mayfield, C. I., & Barker, J. F. Biotransfornation of benzene by denitrification in aquifer sand, Ground Water. 26. 8-14, 1988). They proposed that the addition of nitrate to gasoline-contaminated aquifers would serve as an adjunct to current remedial techniques.
Kuhn et al. disclosed mineralization of toluene, m-xylene, m-cresol and p-cresol in an anaerobic laboratory aquifer column operated under continuous-flow conditions with nitrate as an electron acceptor (Kuhn, E. P., Zeyer, J., Eicher, P, & Schwarzenbach, R. P. Anaerobic degradation of alkylated benzenes in denitrifying laboratory aquifer columns, Applied and Environmental Microbiology, 54, 490-496, 1988). Benzene was not metabolized. Kuhn et al. also confirmed the mineralization of toluene, m-xylene, m-cresol and p-cresol by denitrifiers. Zache and Rehm disclosed the degradation of phenol by a defined mixed culture consisting of Pseudomonas putida F8 and Cryptococcus elinovii H1 under aerobic conditions (Zache & Rehm Degradation of phenol by a coimmobilized entrapped mixed culture, Applied Microbial Biotechnology, 30, 426-432, 1989). Haggblom et al. disclosed metabolism of p-cresol under denitrifying conditions (Higgblom, M. M., Rivera, M. D., Bossert, I. D., Rogers, J. E., & Young, L. Y. Anaerobic biodegradation of para-cresol under three reducing conditions, Microbial Ecology, 20, 141-150, 1990). Phenol was utilized as a slower rate. Evans et al. isolated a denitrifying bacterium that grew on toluene as the sole source of carbon (Evans, P. J., Mang, D. T., Kim, K. S., & Young, L. Y. Anaerobic degradation of toluene by a denitrifying bacterium, Applied and Environmental Microbiology, 57, 1139-1145, 1991). Evans et al. documented the biotransformation of toluene, m-xylene and o-xylene under denitrifying conditions (Evans, P. J., Mang, D. T., & Young, L. Y. Degradation of toluene and m-xylene and transformation of o-xylene by denitrifying enrichment cultures, Applied and Environmental Microbiology, 57, 450-454, 1991). No transformation of benzene or p-xylene was reported. Hegeman and Nickens (in U.S. Pat. No. 5,024,949, Jun. 18, 1991) disclosed bacterium of the genus Pseudomonas which utilizes a branched chain alkyl-substituted aromatic hydrocarbon as its sole carbon and energy source, and which is capable of substantial degradation of trichlorethylene (TCE) under aerobic conditions. The bacterium was described as being capable of denitrification, but the electron donor during denitrification is undisclosed. Also disclosed were methods utilizing the bacterium for the detoxification of TCE-contaminated material. Hutchins disclosed biodegradation of toluene, ethyl benzene, m-xylene and o-xylene under nitrate-reducing conditions. Benzene was not degraded (Hutchins, S. R. Biodegradation of monoaromatic hydrocarbons by aquifer microorganisms using oxygen, nitrate, or nitrous oxide as the terminal electron acceptor, Applied and Environmental Microbiology, August, 2403-2407, 1991). Evans et al. isolated a nitrate-reducing bacterium (NRB), which they named Strain T1, that was capable of mineralization of toluene and o-xylene (Evans, P. J., Ling, W., Goldschmidt, B., Ritter, E. R., & Young, L. Y. Metabolites formed during anaerobic transformation of toluene and o-xylene and their proposed relationship to the initial steps of toluene mineralization, Applied and Environmental Microbiology, February, 496-501, 1992). Khoury et al. reported the anaerobic degradation of p-cresol by a denitrifying culture (Khoury, N., Dott, W. and Kampfer, P. Anaerobic degradation of p-cresol in batch and continuous cultures by a denitrifying bacterial consortium, Applied and Environmental Biotechnology. 37, Feb., 529-531, 1992) and the anaerobic degradation of phenol by a denitrifying culture (Khoury, N., Dott, W. and Kampfer, P. Anaerobic degradation of phenol in batch and continuous cultures by a denitrifying bacterial consortium, Applied and Environmental Biotechnology, 37, February, 524-528, 1992). Coschigano et al. disclosed the metabolism of toluene under denitrifying conditions by a constructed bacterial strain (Coschigano, P. W., Haggblom, M. M., & Young, L. Y. Metabolism of both 4-Chlorobenzoate and Toluene under denitrifying conditions by a constructed bacterial strain, Applied and Environmental Microbiology, 60, 989-995, 1994). Seyfried et al. reported that the denitrifying bacteria Pseudomonas sp. Strain T and Pseudomonas sp. Strain K172 oxidize toluene under denitrifying conditions, and that Strain T also oxidizes m-xylene (Seyfried, B., Glod, G., Schocher, R., Tschech, A., & Zeyer, J. Initial reactions in the anaerobic oxidation of toluene and m-xylene by denitrifying bacteria, Applied and Environmental Microbiology, 60, 4047-4052, 1994). Fries et al. characterized anaerobic toluene degradation under denitrifying conditions (Fries, M. R., Zhou, J., Chee-Sanford, J., & Tiedje, J. M. Isolation, characterization, and distribution of denitrifying toluene degraders from a variety of habitats, Applied and Environmental Microbiology, 60, 2802-2810, 1994).
Dehalogenation by denitrifying cultures has also been reported. Bouwer and McCarty documented the dechlorination of carbon tetrachloride (CT), but not trichloroethane (TCA), under denitrifying conditions (Bouwer, E. J. & McCarty, P. L. Transformations of 1- and 2-carbon halogenated aliphatic organic compounds under methanogenic conditions, Applied and Environmental Microbiology, 45, 1286-1294, 1983). Egli et al. were unable to cause a hydrogen-oxidizing, autotrophic nitrate-reducing bacteria (NRB) to degrade CT (Egli, C., Tschan, T., Scholtz, R., Cook, A. M., & Leisinger, T. Transformation of tetrachloromethane to dichloromethane and carbon dioxide by Acetobacterium woodii, Applied and Environmental Microbiology 54, 2819-2824, 1988). Criddle et al. isolated a denitrifying Pseudomonas sp. (strain KC) that is capable of dechlorinating CT (Criddle, C. S., DeWitt, J. T., Grbic-Galic, D., & McCarty, P. L. Transformation of carbon tetrachloride by Pseudomonas sp. Strain KC under denitrification conditions, Applied and Environmental Microbiology, 56, 3240-3246, 1990). Petersen et al. characterized a denitrifying consortium capable of transforming carbon tetrachloride (Petersen, J. N., Skeen, R. S., Amos, K. M., & Hooker, B. S. Biological destruction of CCl.sub.4 : I. Experimental design and data, Biotechnology and Bioengineering, 43, 521-528, 1994). Hooker et al. described kinetic modeling of biotransformation of carbon tetrachloride by a denitrifying consortium (Hooker, B. S., Skeen, R. S. and Petersen, J. N. Biological destruction of CCI4: II. Kinetic Modeling. Biotechnology and Bioengineering, 44,211-218, 1994). Skeen et al. described a batch reactor that they used to monitor biodegradation of carbon tetrachloride by a denitrifying culture (Skeen, R. S., Truex M. J., Petersen, J. N. and Hill, J. S. A batch reactor for monitoring process dynamics during biodegradation of volatile organics. Environmental Process, 13, 174-177, 1994).
Other background material is provided in a report by Yellowstone Environmental Science, Inc., of 920 Technology Blvd., Bozeman, MT 59715, entitled "Biomimetic Process for Hazardous Waste Remediation, Phase I Final Technical Report, August, 1992." That report is incorporated by reference herein as if fully set forth.